from abc import ABC, abstractmethod #import the module for abstract

class Animal(ABC):
    @abstractmethod # indicating that this method must be implemented by subclass
    def sound(self):  # require subclass to achieve
        pass

class Dog(Animal):
    def sound(self):
        return "wolf!"

class Cat(Animal):
    def sound(self):
        return "Meow!"

dog = Dog()
cat = Cat()
#animal = Animal() #animal is an abstract class,could not be called

print(dog.sound())
print(cat.sound())